Method for producing zinc casings for batteries and the like



jufiy 18, 1967 G- M ROBE ET AL 3,331,122

METHOD FOR PRODUCING ZINC CASINGS FOR BATTERIES AND THE LIKE Filed Jan. 11, 1965 CASTING CLEANING E LUBR/CA TING IMPACT EXTRUD/NG United States Patent 3,331,122 METHOD FOR PRODUCING ZINC CASINGS FOR BATTERIES AND THE LIKE Gordon M. Robb and R. Fraser Code, Islington, Ontario, Canada, assignors to Union Carbide Canada Limited, Toronto, Ontario, Canada, a company of Canada Filed Jan. 11, N65, Ser. No. 424,855 18 Claims. (Cl. 29-528) This invention relates to the casting of zinc slugs which are impact extrudable without rolling, to impact extrudable cast zinc slugs which can be impact extruded without rolling, and to processes for forming zinc slugs into cans for batteries involving the impact extrusion of cast zinc slugs.

Zinc cans for dry cell batteries commonly are impact extruded from zinc slugs, or calots, which have been blanked previously from sheets of rolled zinc. In order to produce such zinc slugs, the zinc is melted and cast into billets. The billets, usually 1 /2" to 3" thick, are preheated, e.g. to a temperature between 300' F. and 500 F. and then are rolled into sheets of the desired thickness, usually 0.125" to 0.250", in seven to twelve passes. After rolling the sheets are blanked in a punch press to form rolled zinc slugs that have a fine grain structure and are capable of being impact extruded.

Cast Zinc has a coarse, columnar grain structure which is altered by rolling to a fine grain structure. In order for a metal slug to be impact extrudable it has been thought necessary, in the past for the metal slug to have a fine-grain metallurgical structure, and the techniques have been developed for the casting of metals like magnesium or aluminum into slugs which can be impact extruded without any prior rolling of the slugs. By practising such techniques aluminum or magnesium slugs having the fine-grain metallurgical structure required are produced.

Notwithstanding these developments it has not been thought that cast zinc slugs could be impact extruded successfully without prior rolling, because cast zinc slugs have a coarse columnar grain structure, as aforementioned, which always has been considered exactly opposite to the grain structure required for impact extrusion.

In accordance with one aspect of this invention it has been discovered unexpectedly that zinc slugs cast in a particular way can be impact extruded, nothwithstanding the fact that the grain structure of such cast zinc slugs is coarse and columnar. This is quite unexpected, since, as aforementioned, it always has been thought that only metals having a fine-grain metallurgical structure could be impact extruded. It is perhaps even more unexpected in view of the fact that not even conventionally die cast zinc slugs can be satisfactorily impact extruded directly. Such slugs have been found to explode in an impact extrusion machine.

It is one object of this invention to provide a process for producing cast zinc slugs which are impact extrudable without any prior rolling, thereby providing a process which permits impact extrudable zinc slugs to be produced without the previously followed steps of casting into billets, preheating the billets, rolling the preheated billets and blanking the rolled zinc sheet into slugs.

It is another object of this invention to provide a process for forming zinc cans for batteries which does not require the use of rolled zinc slugs, and yet which employs impact extrusion of a zinc slug in the forming ste lh accordance with one aspect of this invention there is provided a cast zinc slug in the form of a generally circular disc having two, opposite, substantially parallel, generally circular faces and a generally circular side edge. The grain structure of the zinc slug is coarse and columnar. The grain of the Zinc slug inwardly of its side edge and to the centre of the slug is oriented substantially normal to the circular faces of the slug. The grain of the slug at and adjacent to its side edge is oriented so as to be substantially normal to the side edge.

In accordance with another aspect of this invention, it has been found that such a slug unexpectedly can be formed into a zinc can for a battery by impact extruding the zinc slug, no rolling of the slug being required. While it is not known for certain, it is believed that the grain orientation of a cast zinc slug is the governing feature in determining whether or not the cast zinc slug will be impact extrudable, and it is believed that the aforementioned orientation of the grain at the side edges of a cast zinc slug embodying this invention is instrumental in preventing the large columnar crystals from separating from each other during impact extrusion, thereby forming undesirable faults or cracks in the cans. In this connection it has been fuond that if a zinc slug is cast in such a manner that the grain of its crystals runs between the two faces of the slug throughout the whole slug, such a slug cannot be successfully impact extruded as cracks appear in the finished can, presumably due to breaking of the slug along its grain adjacent to the edge of the slug.

In accordance with another aspect of this invention, there is provided a process for making a cast, impact extrudable zinc slug which comprises maintaining a temperature differential between oppositely-disposed faces of the slug of zinc being cast during the casting of the slug, the differential being suflicient so solidify the moulten zinc into an impact extrudable slug of zinc having the above-mentioned coarse and columnar grain structure.

This invention will become more apparent from the following detailed description, taken in conjunction with the appended drawings, in which:

FIGURE 1 is a perspective view of an impact extrudable cast zinc slug produced in accordance with this invention, a part of the slug being broken away to reveal the grain structure and grain orientation thereof,

FIGURE 2 is a block diagram showing the steps which are followed in producing a zinc battery can in accordance with this invention,

FIGURE 3 is a perspective view of the two parts of a mould which may be used in casting impact extrudable zinc slugs in accordance with this invention,

FIGURE 4 is a perspective view showing the casting made in the mould of FIGURE 3, and

FIGURE 5 is a schematic representation of the die and punch of a conventional impact extrusion machine.

Referring to FIGURE 1 there is shown a zinc slug or calot 10 made in accordance with this invention and capable of being impact extruded without rolling. The zinc slug is in the form of a generally circular disc having two, opposite, substantially parallel, generally circular faces 11 and 12 and a generally circular side edge 13. The slug is void-free and hence solid. The absence of voids in the casting is of considerable importance, since slugs containing appreciable voids therein cannot be impact extruded successfully.

The grain structure of slug 10 is coarse and columnar, as compared to the fine, granular structure of rolled zinc.

The grain direction of slug 10 inwardly of side edge 13 to the centre of slug 10 is oriented substantially normal to faces 11 and 12, as seen at 14. On the other hand, the grain direction of slug 10 adjacent to and at side edge 13 is oriented so as to be essentially normal to the side edge 13 and the other grain direction, as seen at 15.

The composition of the zinc slug 10 is usually 99% by weight zinc, the remaining 1% being primarily lead and cadmium, which are employed as grain refiners, with small amounts of such impurities as iron, tin and copper. Lead (Catt-1.0%) and cadmium (0.040.07%) commonly are added to pure electrolytic zinc in order to provide the most suitable slug for forming into battery cans. Alternatively prime western zinc may be employed. Although the above analysis is usually used for battery cans, other compositions, e.g. pure electrolytic and zinc-titanium alloys, can be impact extruded for other applications.

Slug of FIGURE 1 has been made on a laboratory scale in a mould of the type shown in FIGURE 3. Mould 15 has a cover or top 16 in the form of a rectangular block and a bottom 17, also in the form of a rectangular block, but recessed to form a block-like cavity 18 defined by lips 19. There is an opening 19a in one of lips 19 through which moulten metal may be poured into the mould. Set into block 16 is an asbestos washer 16a of the same width as lips 19. This washer forms a thermal barrier between the two blocks 16 and 17. Two disc-shaped cavities 21 are provided in block 17 opening into and extending downwardly from surface 20. The depth of cavity 18 may be of the order of for example, while the depth of cavities 21 may be of the order of 0.15, for example, to produce a slug which can be formed into a size D battery can.

In casting a zinc slug 10 embodying this invention it is important, during the solidification of the slug, to maintain the surface of the mould that is in contact with one face of the slug at a temperature higher than about 100 F. below the melting point of the moulten zinc poured into the mould, and to maintain the surfaces of the mould in contact with the side edges and the other face of the slug at a temperature less than that of the other mould surface to provide a temperature differential sufiicient to solidify the moulten zinc into an impact-extrudable slug of zinc having the desired coarse, columnar grain structure. With the mould 15 of FIGURE 3 this may be achieved by electrically or otherwise heating block 16, and by running cooling water through coolant passages (not shown) in block 17. A temperature of the one surface higher than 50" F. below the melting point of the moulten zinc is preferred. In this manner a temperature differential is maintained across the slug, which then solid ifies from the cold sides towards the hot side.

While it is important, during solidification of the slug, for one surface of the mould in contact with a face of the slug to be maintained higher than about 100 F. below the melting point of the moulten zinc being cast, if desired the temperature of the hot surface of the mould may be above the melting point of the moulten zinc, but it should not be so high as to prevent proper solidification of the slug. There is no particular advantage to be gained by employing temperatures substantially in excess of the melting point of the moulten zinc being cast, and,

indeed, such a procedure would involve additional heat-' ing costs and require more time for solidification to be accomplished.

The temperature of the cold mould surfaces is not critical. Temperatures as low as 45 F. have been successfully employed, for example. However, the cold surfaces should not be cold enough to cause dew-point condensation or freeze the metal before the mould is filled. In general, however, large temperature differentials of the order of several hundred degrees F. and preferably more are desirable because of the more rapid solidification of the metal.

In using a mould 15 of the type shown in FIGURE 3, and in which blocks 16 and 17 may be fabricated from graphite, for example, block 17 is cooled as required, block 16is heated as required, and the moulten zinc is poured into the mould cavity through opening 19a. After solidification a casting 22 (FIGURE 4) is provided. The thin plate 23 of this casting may be broken ofi from around slugs 10.

From a commercial point of view slugs 10 can be cast using apparatus of the type disclosed in United States Patents 2,863,188, G. Harrison, Dec. 9, 1958, or 2,923,- 040, C. L. Goodwin et al., Feb. 2, 1960, and reference is made thereto.

Referring now to FIGURE 5, the punch 24 and die 25 of a commercially available impact extrusion machine for impact extruding zinc slugs into cans for batteries are shown. This machine may be of a conventional type manufactured in Germany by Herlan & Co. or Schuler, for example.

Die 25 includes an annular steel member 26 in which is mounted an annular tungsten carbide member 27. A steel back-up plate 28 is fixed to member 26 and has a cylindrical projection 29 that is inserted into the opening in member 26, projection 29 having a surface 30 against which one face of slug 10 abuts during extrusion. Any suitable and well-known means are employed to sequentially feed slugs into the recess 31 in die 25.

Punch 24 is cylindrical in nature with a slightly flanged tip and is reciprocated back and forth in the direction shown by the arrow. On its forward stroke it compresses slug 10 against surface 30 under sufiicient pressure that the slug flows or its extruded over the outer surface of punch 24 in the form of a can. This can is removed from punch 24 during the backward stroke of punch 24 when the can strikes a fixed sleeve 32 in which punch 24 reciprocates.

In accordance with this invention there is provided a process for manufacturing zinc cans for batteries which eliminates the steps of casting and preheating of zinc billets, rolling the zinc billets into sheets and blanking the cold rolled sheets. This process is illustrated in FIG- URE 2 to which reference is now made. Zinc slugs 10 are cast as hereinbefore specified. The slugs then. may be cleaned, if necessary. The cleaning step is conventional in nature and is practised with rolled zinc slugs. The cleaning may be effected by tumbling the slugs in sawdust, or by degreasing or washing. This cleaning step may not be necessary in many cases, since cast, impact extrudable slugs which are clean can be obtained directly fromthe mould, whereas rolled zinc slugs must be cleaned after rolling and blanking because of the large amounts of lubricant used during the rolling operation.

Before the cast zinc slugs are impact extruded they should be lubricated, as indicated in FIGURE 2. This is a conventional step used with rolled zinc slugs before impact extrusion thereof. Many suitable lubricants are available, e.g., lard oil dissolved in a suitable solvent, graphite, or mixtures of the foregoing.

Once the cast zinc slugs have been lubricated, they then can be impact extruded, as indicated in FIGURE 2.

Impact extrusion of the zinc slugs into cans for batteries can be carried out in the conventional manner previously noted herein.

It will be appreciated that cans may be produced in accordance with this invention for uses other than in batteries, e.g., as containers for condensers or other electronic or electrical components. Furthermore, the slugs produced in accordance with this invention need not be disc shaped but could be hexagonal or assume other configurations.

While preferred embodiments of this invention have been disclosed herein, those skilled in the art will appreciate that changes and modifications may be made therein without departing from the spirit and scope of this invention as defined in the appended claims.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as folows:

1. A cast zinc slug having two opposite, faces and side edges extending between said faces, the grain structure of said cast zinc slug being coarse and columnar, the grain direction of said cast Zinc slug inwardly of said side edges to the centre of said cast zinc slug being I oriented to intersect said faces, the grain direction of said cast zinc slug at and adjacent to said side edges being oriented substantially normal to said side edges and towards the first-mentioned grain direction of said cast zinc slug.

2. A cast zinc slug capable of being impact extruded and in the form of a substantially void-free, solid slug having two opposite faces and side edges extending between said faces, the grain structure of said cast Zinc slug being coarse and columnar, the grain direction of said cast zinc slug inwardly of said side edges to the centre of said cast zinc 'slug being oriented to intersect said faces, the grain direction of said cast zinc slug at and adjacent to said side edges being oriented substantially normal to said side edges and towards the firstmentioned grain direction of said cast zinc slug.

3. A cast zinc slug capable of being impact extruded and in the form of a generally circular substantially voidfree solid disc having two opposite substantially parallel generally circular faces and a generally circular side edge, the grain structure of said cast zinc slug being coarse and columnar, the grain direction of said cast zinc slug inwardly of said side edge and to the centre of said cast zinc slug running substantially normal to said faces, the grain direction of said cast zinc slug at and adjacent to said side edge being substantially normal to said side edge and oriented towards the first-mentioned grain direction.

4. A process for forming a zinc can by impact extrusion of a cast zinc slug which comprises impact extruding into a can a cast, substantially void-free, zinc slug having two opposite substantially parallel faces and a side edge therebetween, the grain structure of said cast zinc slug being coarse and columnar, the grain direction of said cast zinc slug inwardly of said side edge and to the centre of said cast zinc slug running substantially normal to said faces, the grain direction of said cast zinc slug at and adjacent to said side edge being substantially normal to said edge and oriented towards the first-mentioned grain direction.

5. A process for forming a zinc can by impact extrusion of a cast zinc slug which comprises, providing a die having a cylindrical recess defined by side walls and a bottom wall, providing a cast zinc slug as defined in claim 3, placing said cast zinc slug in the recess with one of said faces parallel to said bottom wall, and impact extruding said cast zinc slug into a can by driving a cylindrical punch against the other one of said faces with sufiicient force to compress said cast zinc slug against said bottom wall and extrude said cast Zinc slug over said punch in the form of a can.

6. A process for forming a zinc can by impact extrusion of a cast zinc slug which comprises, providing a die having a cylindrical recess defined by said side walls and a bottom wall, providing a cast zinc slug as defined in claim 3, lubricating said cast zinc slug, placing the lubricated cast zinc slug in the recess with one of said faces parallel to said bottom wall, and impact extruding said cast zinc slug into a can by driving a cylindrical punch against the other one of said faces with sufiicient force to compress said cast zinc slug against said bottom wall and extrude said cast zinc slug over said punch in the form of a can.

7. A process for casting a zinc slug capable of being impact extruded and in the form of a generally circular substantially void-free solid disc having two opposite substantially parallel generally circular faces and a generally circular side edge which comprises, providing a mould having a generally disc-shaped cavity defined by two opposite generally parallel surfaces and a generally circular side edge, filling the cavity with molten zinc, during solidifying of said molten zinc maintaining one of said surfaces at a temperature at least as high as 100 F. below the melting point of said zinc, and cooling and solidifying the molten zinc by maintaining the other of said surfaces and said side edge defining said cavity at a temperature less than the melting point of said zinc during solidifying of said molten zinc.

8. A process for casting a zinc slug capable of being impact extruded and in the form of a substantially voidfree solid slug having two opposite faces and side edges extending between said faces which comprises, providing a mould having a cavity defined by two opposite surfaces and side edges, filling the cavity with molten zinc, during solidifying of said molten zinc maintaining one of said surfaces at a temperature at least as high as F. below the melting point of said zinc, and cooling and solidifying the molten zinc by maintaining the other of said surfaces and said side edges defining said cavity at a temperature less than the melting point of said Zinc during solidifying of said molten zinc.

9. A process according to claim 8 in which said one surface is maintained at a temperature higher than 50 F. below the melting point of the zinc.

10. A process for casting a zinc slug capable of being impact extruded and in the form of a generally circular substantially void-free solid disc having two opposite substantially parallel generally circular faces and a generally circular side edge which comprises, providing a mould having a generally disc-shaped cavity defined by two opposite generally parallel surfaces and a generally circular side edge, filling the cavity with molten zinc, and during solidifying of said molten zinc maintaining a temperature differential between one of said surfaces and said side edge of said cavity and the other of said surfaces sufficient to solidify said molten zinc into a generally circular substantially void-free solid disc having two opposite substantially parallel generally circular faces, a generally circular side edge, a coarse columnar grain structure, a grain direction inwardly of said side edge of said slug to the centre of said slug running substantially normal to said faces, and a grain direction at and adjacent to said side edge of said slug substantially normal to said side edge of said slug and oriented towards the firstmentioned grain direction.

11. A process for casting a zinc slug capable of being impact extruded and in the form of a substantially voidfree solid slug having two opposite faces and side edges extending between said faces which comprises, providing a mould having a cavity defined by two opposite-surfaces and side edges, filling the cavity with molten zinc, and during solidifying of said molten zinc maintaining a temperature differential between one of said surfaces and said side edges of said cavity and the other of said surfaces sufficient to solidify said molten zinc into a substantially void-free solid slug having two opposite faces, side edges extending between said faces, a coarse columnar grain structure, a grain direction inwardly of said side edges of said slug to the centre of said slug oriented to intersect said faces, and a grain direction at and adjacent to said side edges of said slug oriented substantially normal to said side edges and towards the first-mentioned grain direction.

12. A process for forming a zinc can which comprises casting a substantially void-free zinc slug capable of being impact extruded and having two opposite substantially parallel faces and a side edge extending therebetween by providing a mould having a cavity defined by two opposite generally parallel surfaces and a side edge extending therebetween, filling the cavity with molten zinc, during solidifying of said molten zinc maintaining one of said surfaces at a temperature at least as high as 100 F. below the melting point of said zinc, cooling and solidifying the molten zinc by maintaining the other of said surfaces and said side edge defining said cavity at a temperature less than the melting point of said zinc during solidifying of said molten zinc, removing the cast zinc slug from said mould, and impact extruding said cast zinc slug into a can without previously rolling said cast zinc slug.

13. A process according to claim 12 including the step of lubricating said cast zinc slug before impact extruding said cast zinc slug.

14. A process according to claim 13 in which the temperature of said one surface is higher than 50 F. below the melting point of said zinc.

15. A process according to claim 13 wherein said cast zinc slug is impact extruded by providing a die having a recess defined by side walls and a bottom wall, placing said cast Zinc slug in the recess with one of said faces parallel to said bottom wall, and impact extruding said cast zinc slug into a can by driving a punch against the other one of said faces with sufficient force to compress said cast zinc slug against said bottom wall and extrude said cast zinc slug over said punch in the form of a can.

16. A process for forming a zinc can which comprises casting a zinc slug capable of being impact extruded and in the form of a generally circular substantially voidfree solid disc having two opposite substantially parallel generally circular faces and a generally circular side edge by providing a mould having a generally disc-shaped cavity defined by two opposite generally parallel surfaces and a generally circular side edge, filling the cavity with molten zinc, during solidifying of said molten zinc maintaining a temperature differential between one of said surfaces and said side edge of said cavity and the other of said surfaces sufiicient to solidify said molten Zinc into a generally circular substantially void-free solid disc having two opposite substantially parallel generally circular faces, a generally circular side edge, a coarse columnar grain structure, a grain direction inwardly of said side edge of said sing to the centre of said slug running substantially normal to said faces, and a grain direction at and adjacent to said side edge of said slug substantiall normal to said side edge of said slug and oriented towards the first-mentioned grain direction, removing the cast Zinc slug from said mould, and impact extruding said cast zinc slug into a can without previously rolling said cast zinc slug.

17. A process according to claim 16 including the step of lubricating said cast zinc slug before impact extruding said cast Zinc slug.

18. A process according to claim 17 wherein said cast zinc slug is impact extruded by providing a die having a cylindrical recess defined by side walls and a bottom wall, placing said cast zinc slug in the recess with one of sad faces parallel to said bottom wall, and impact extruding said cast zinc slug into a can by driving a cylindrical punch against the other one of said faces with sufiicient force to compress said cast zinc slug against said bottom wall and eXtrude said cast zinc slug over said Punch in the form of a can.

References Cited UNITED STATES PATENTS 1,492,230 4/1924 Towne 72266 X 1,777,659 10/1930 Stay et al. 22-2l2 1,850,477 3/1932 Roth 22--212 2,042,735 6/1936 Scheil 22-212 X 2,578,407 12/ 195 l Ebeling.

3,234,609 2/1966 Madono 22-212 X 1 JOHN F. CAMPBELL, Primary Examiner.

J. L. CLINE, Assistant Examiner. 

16. A PROCESS FOR FORMING A ZINC CAN WHICH COMPRISES CASTING A ZINC SLUG CAPABLE OF BEING IMPACT EXTRUDED AND IN THE FORM OF A GENRALLY CIRCULAR SUBSTANTIALLY VOIDFREE SOLID DISC HAVING TWO OPPOSITE SUBSTANTIALLY PARALLEL GENERALLY CIRCULAR FACES AND A GENERALLY CIRCULAR SIDE EDGE BY PROVIDING A MOULD HAVING A GENERALLY DISC-SHAPED CAVITY DEFINED BY TWO OPPOSITE GENERALLY PARALLEL SURFACES AND A GENERALLY CIRCULAR SIDE EDGE, FILLING THE CAVITY WITH MOLTEN ZINC, DURING SOLIDIFYING OF SAID MOLTEN ZINC MAINTAINING A TEMPERATURE DIFFERENTIAL BETWEEN ONE OF SAID SURFACES AND SAID SIDE EDGE OF SAID CAVITY AND THE OTHER OF SAID SURFACES SUFFICIENT TO SOLIDIFY SAID MOLTEN ZINC INTO A GENERALLY CIRCULAR SUBSTANTIALLY VOID-FREE SOLID DISC HAVING TWO OPPOSITE SUBSTANTIALLY PARALLEL GENERALLY CIRCULAR FACES, A GENERALLY CIRCULAR SIDE EDGE, A COARSE COLUMNAR GRAIN STRUCTURE, A GRAIN DIRECTION INWARDLY OF SAID SIDE EDGE OF SAID SLUG TO THE CENTRE OF SAID SLUG RUNNING SUBSTANTIALLY NORMAL TO SAID FACES, AND A GRAIN DIRECTION AT AND ADJACENT TO SAID SIDE EDGE OF SAID SLUG SUBSTANTIALLY NORMAL TO SAID SIDE EDGE OF SAID SLUG AND ORIENTED TOWARDS THE FIRST-MENTIONED GRAIN DIRECTION, REMOVING THE CAST ZINC SLUG FROM SAID MOULD, AND IMPACT EXTRUDING SAID CAST ZINC SLUG INTO A CAN WITHOUT PREVIOUSLY ROLLING SAID CAST ZINC SLUG. 